SMTP DoS settings (methodology)

Question

Have already been referred here: 
 https://doc.sophos.com/nsg/sophos-firewall/19.5/help/en-us/webhelp/onlinehelp/AdministratorHelp/Email/GeneralSettings/index.html#smtp-settings 
 I wonder if any of you guys can share with me what and why your settings are for: 
 
 Max Connections 
 Maximum Connections / Host 
 Max emails / connection 
 max recipients / email 
 Emails rate 
 Connections rate 
 
 I have a single on premise exchange server behind the firewall.

emmosophos · Answer

Hello there, 
 Thank you for contacting the Sophos Community. 
 I'd recommend you contact your Sales Engineer/Professional Services to help you determine the value of each setting for your environment. 
 They&rsquo;ll vary for any deployment since it is not the same to set Max Connection for a Firewall that only works as an MTA than one that works as web Filter with encryption enabled and a high number of employees since this value involves or you have to take in consideration the CPU, Memory, Network, etc. 
 The maximum connection per host, should be calculated on the expected usage patterns. 
 Max Emails per connection: this one should be calculated by calculating your email server capacity and underlayer network. 
 The rest are more self-explanatory based on the Documentation. Still, again, I recommend you talk to your Sales Engineer/Prof Service so they can assist you in tweaking the setting after surveying your email traffic. However most people that uses the setting just leave them the default values. 
 Regards,